Composite electric element of silver-cadmium oxide alloy contact

ABSTRACT

A composite electric contact element is disclosed comprising a contact material formed of an alloy of silver-cadmium oxide, the element having a contact face and an opposite face composed of a silver layer with cadmium oxide particles distributed in between, such that the concentration of cadmium oxide particles increases from a minimum at the contact face to a maximum towards the face with the silver layer.

United States Patent [72] Inventor Akira Shibata Tokyo, Japan [2]] Appl No 815,677 [22] Filed Apr. 14, 1969 [45] Patented July 27, 1971 [73] Assignee Chugai Electric Industrial Co., Ltd.

Tokyo, Japan 54] COMPOSITE ELECTRIC ELEMENT 0F SILVER- CADMIUM OXIDE ALLOY CONTACT 3 Claims, 7 Drawing Figs.

[52] U.S.Cl 200/166C [5i] lnt.Cl a a. 110lb 1/02 [50] Field of Search 200/166 C; 29/630 C [56] References Cited UNITED STATES PATENTS 2,425,053 8/1947 Swinehart 200/166 C X 2,468,888 5/1949 Mekelburg 200/166 C 3,1 14,631 12/1963 Sistarc et al. 200/166 C X 3,154,660 10/1964 Witherspoon 209/630 C X FOREIGN PATENTS 99l,433 5/1965 Great Britain......v.....t. ZOO/166C Primary ExaminerH. 0. Jones Atl0rney-Sandoe, Hopgood & Calimafde ABSTRACT: A composite electric contact element is disclosed comprising a contact material formed of an alloy of silver-cadmium oxide, the element having a contact face and an opposite face composed of a silver layer with cadmium oxide particles distributed in between, such that the concentration of cadmium oxide particles increases from a minimum at the contact face to a maximum towards the face with the silver layer.

PATENTEU JUL2 7 l97| 2 INVENTOR Almw swan r24 BYMIWJW ATTORNEYS COMPOSITE ELECTRIC ELEMENT OF SILVER- CADMIUM OXIDE ALLOY CONTACT The present invention relates to a new composite electric contact and a process of producing said composite electric contact. More particularly, the present invention relates to a new composite electric contact contact employing an alloy of silver-cadmium oxide as a contact material and having a silver layer at an opposite face in relation to the contact face thereof, and to a process of producing said composite electric contact by internal oxidation of the contact material.

The conventional processes of producing a contact material of an alloy of silver-cadmium oxide are generally classified into a sintering method by power metallurgy and a method by internal oxidation of alloy. The internal oxidation method is, as well known, a process of obtaining a contact material of alloy of silver-cadmium, by subjecting said alloy of silver-cad mium to an oxygen atmosphere at a high temperature and causing oxidation of cadmium or other metal contained in said alloy from a circumferential area of the contact material. Alloy of silver-cadmium oxide, however, has generally a problem in brazing to brass or phosphor bronze used as a backing metal, or a spring material. There are two methods in practice for solving the problem. One is a method of applying a silver layer onto a brazing face of a contact material, wherein the silver layer is generally pressure bonded to alloy of silver-cadmium. According to this method, since oxidation progresses towards an internal area from a circumferential area of a contact material, a belt of layerlike area of thin oxide is seen around a central portion in its sectional area due to the oxidation propensity of the silver-cadmium alloy. The thus-obtained contact material, when practically used as a contact, often shows serious defects in which the amount of wear greatly increases as wear of the contact develops from the contact face to the area of thin oxide, and weldability becomes poor.

Another method is generally called a one-face oxidation method, in which one face of a contact, namely a brazing surface, is maintained unoxidized. The method is to make use of the fact that oxidation progresses inwardly from the circumferential area or portion towards the internal area of the contact material. In this method, two pieces of contact material which are mated one with another, prior to oxidation, may be welded at their mated faces, and subjected to an oxygen atmosphere only for a predetermined period of time, in such a manner as to leave one face of the contact material unoxidized. Suchprocess involves practically a technical problem in welding miniature contacts one by one. It is a general practice to weld two sheets of contact material of alloy of silvercadmium at their mated faces, prior to oxidation, then separate the two sheets of contact material one from another, after oxidation, and finally cut each sheet to a given size. This still involves another problem that the period of oxidation must be reduced, since the mated faces of two sheets of contact material are essentially maintained unoxidized so as to provide a brazing face in the finished contact, and consequently a desired oxidation area or thickness is hardly obtained.

Accordingly, a primary object of the present invention is to provide a new composite electric contact of a silver'cadmium oxide alloy which overcomes the disadvantages conventional contacts, and a process of producing said composite electric contact.

The process for producing a composite electric contact containing alloy of silver-cadmium as a contact material comprises; mating an antioxidation or barrier layer closely with one face of the contact material serving as a contact face of a finished composite contact and having a silver layer bonded for convenience of brazing to the face opposite the contact face; subjecting said contact material to an oxygen at mosphere at a high temperature so as to cause oxidation of cadmium or other constituents contained in said alley; and,

after a predetermined oxidation of cadmium or other metal constituents is attained, taking said contact material out of the oxygen atmosphere and separating the antioxidation or barrier layer from the contact face as a result, the oxidation of cadmium in the oxygen atmosphere progressing or developing towards an internal area of the contact material from an entire surface including the silver layer face, other than the antioxidation layer, thereby forming, within the contact material, a layer of cadmium oxide particles distributed thinly or at a lower concentration adjacent to the contact face and thickly or at a higher concentration progressively towards the silver layer face.

The thus obtained new composite electric contact of the present invention has an advantage of providing a constantly equal contact resistance over an entire period of its life, due to such advantageous progressive distribution of cadmium oxide within the contact material, since an area showing relatively thinner or lower distribution of cadmium oxide particles appears on the contact face before wear at the contact face has yet occurred where pressure of the backing material exerted on the contact face is larger; and when and as wear at the contact face develops on and pressure of the backing material exerted on the contact face is reduced progressively, an area showing progressively thicker or greater concentration of cadmium oxide begins to appear on the contact face.

In the accompanying drawings;

FIG. 1 is an enlarged sectional view of a composite contact element according to the present invention;

FIG. 2 is an explanatory view showing in what directions oxidation progresses on a contact face of a composite contact element of the present invention;

FIG. 3 is a perspective view of one embodiment of the present invention, showing a state of a contact material subjected to an oxygen atmosphere;

FIG. 4 is a perspective view of another embodiment of a contact material according to the present invention;

FIG. 5 is a sectional view showing a state of oxidation of a contact element produced according to the firstly mentioned known art;

FIG. 6 is a sectional view showing a state of oxidation of a contact element produced according to the secondly mentioned known art; and

FIG. 7 is a sectional view showing a state of oxidation of a composite contact element according to the present invention.

Description will be made with reference to the accompanying drawings. In FIGS. 1 through 3, numeral 1 is a piece of alloy of silver-cadmium which is used as a contact material. Numeral 2 is a layer of silver, which has a thickness sufficient to weld the contact material to a backing or spring material, or of one-eighth to one-tenth to that of alloy of silver-cadmium and is pressure bonded to one face of said piece of alloy. Numeral 3 is a film or barrier layer of any metal such as nickel, chromium, aluminum, copper, iron, alloy of such metal, salts thereof or glass which can serve as an antioxidation or barrier layer in an oxygen atmosphere at a high temperature. The purpose of the barrier layer is to resist diffusion of oxygen into the substrate at the barrier layer side. The layer of nickel, chromium, aluminum, copper, iron, alloy of such metal, salts thereof or glass is pressure bonded to the face, (contact-forming face) opposite to the silver layer bonded face of the piece of alloy of silver-cadmium, in a thickness of 10 to I00 ;I.. The layer of such metal or alloy which is used only for antioxidation of the contact face, is essentially required to have a thickness sufficient to prevent or inhibit oxidation of the contact face, but not more than that. Bonding of this layer may be achieved by pressure bonding, plating or vaporizing. The thus-prepared contact material is processed into a desired contact shape, which is then subjected to an oxygen atmosphere at a high temperature. After a predetermined oxidation of the contact material is attained, the antioxidant or barrier layer is removed from the contact face by pincers or a severing treatment, thereby obtaining a desired contact.

FIG. 4 which is another example of a composite contact produced by another process, shows two plates of an alloy of silver-cadmium l, 1' each having a silver layer 2 pressure bonded to one face the two plates being mated with their silver layer faces disposed outwardly, and welded at mated faces 4 into a single composite plate. The thus-prepared metal plate is then subjected to an oxygen atmosphere at a high temperature so as to cause oxidation of said metal plate. After a predetermined amount of oxidation is attained, the metal composite plate is separated one from another and processed into a desired shape of contact.

The composite contact having a construction as shown in FlG. l and an internal area at which oxidation of metal or alloy of such metal progresses in the direction of the arrows as shown in FIG. 2 has a below-mentioned characteristic in comparison with those produced by conventional processes. In the composite contact produced by the firstly mentioned conventional method, oxide in the contact material has particles increasing in size towards the central sectional area which parti cles are distributed somewhat thinly around the central area as shown in FIG. 5, since oxidation ofa metal constituent, in this method, occurs at a circumferential area and progresses inwardly towards the central area of the contact material having a silver layer pressure bonded to one face of the contact material. This results in a hardness increase around the circumferential area which decreases towards the central area. Another conventional composite contact produced by the secondly mentioned one-face oxidation method results in a hardness increase in the facing area which decreases towards the brazing surface, as shown in FIG. 6. On the contrary, the composite contact according to the present invention has hardness which is lower in the facing area and which increases towards the brazing face, as shown in FIG. 7. This advantageously provides stable contact resistance of the composite contact. Three kinds of composite contact, if comparison is made in respect of wear, respectively show the following features. That is, the firstly mentioned conventional composite contact shows greatly increased rate of wear around the central sectional area, and the secondly mentioned conventional composite contact shows a tendency that a rate of wear increases according to reduction in thickness of the contact due to wear. Meanwhile, the composite contact ofthe present invention tends to increase in wear resistance as the contact is reduced in thickness according to progress of wear.

EXAMPLEI A plate of silver-calmium alloy (cadmium 13 percent) with a 18mm. thickness, a 30mm. width and a 100mm. length, having a silver layer with a 2mm. thickness, a 30mm. width and a 100mm. length, bonded to one face, and a layer of nickel with a 0.1mm. thickness, a 30mm. width and a lOOmm. length bonded to an opposite face (contact-forming facing), was subjected to rolling into a plate of L5 mm. in thickness. After that, the l.5-mm. thick plate was punched out into disc pieces each having a 8mm. diameter. The disc piece was subject to an oxygen atmosphere at a normal atmospheric pressure and at a temperature of 800 C. for 96 hours. After oxidation being finished, nickel oxide formed on the plate surface was removed by pincers, thereby producing a composite contact of the present invention as set forth in the foregoing passage. The thus-obtained composite contact was mounted to an electromagnetic contactor, and tested on contact resistance, when wear at the contact face is respectively 0 percent, 25 percent, 50 percent and 75 percent. Furthermore, the same test on contact resistance was applied to the conventional composite contact having a 8mm. diameter and a 1.5mmv thickness and formed of silver-cadmium oxide alloy (cadmium 13 percent) which was prepared by the firstly mentioned conventional process of causing oxidation from the circumferential area of the contact material having a silver layer bonded to one face, under the same oxidation condition as in the above example. Test results on contact resistance of respective composite contacts are shown in table I.

Table l Contact Resistance Wear 0% Wear 25% Wear 50% Wear 75% The invented composite contact 25 m. 9 8 m. (1 l0 m. 0 l5 m. (I

The conventional composite Contact IO m. (l 15 m. n 20 m. ll 25 m. I}

Results of life test of said two composite contacts are shown in table ll. Table ll clearly shows that life of composite contact of present invention is increased by about 30 percent, compared with that ofthe conventional one.

A plate of silver-cadmium alloy (cadmium 13 percent) with a 18mm. thickness, a 30mm. width and a mm. length, having a silver layer with a 2mm. thickness, a 30mm. width and a 100mm. length bonded to one face, was subject to rolling into a l.5-mm. thick plate. The thus-rolled plate was plated with chromium of 0.01 mm. in thickness at one face (contact-forming face) opposite to the silver layer face. Subsequently, the plate was subject to an oxygen atmosphere at a normal atmospheric pressure and at a temperature of 800 C. for 96 hours. After oxidation being finished, the plate was punched out into disc pieces each having a 8mm. diameter, thereby producing a composite contact of the present invention as set forth.

The thus-obtained composite contact was mounted to an electromagnetic contactor, and tested on contact resistance when wear at the contact face is respectively 0 percent, 25 percent, 50 percent and 75 percent. The same test on contact resistance was applied to the conventional composite contact having a 8mm. diameter and a 1.5mm. thickness and formed of silver-cadmium oxide alloy (cadmium 13 percent) which was produced by causing oxidation from the circumferential area of the contact material having a silver layer applied to one face, under the same oxidation condition as in the above example ll. Test results are shown in table lll.

Table III Contact resistance Test results on life of both composite contacts are shown in table IV. It clearly shows that life of the invented composite contact is increased by about 32 percent, compared with that of the conventional one.

A plate of silver-cadmium alloy (cadmium 13 percent) with an 18mm. thickness, a 30mm. width and a 100mm. length, having a silver layer with a 2mm. thickness, a 30mm. width and a 100mm. length bonded to one face, was rolled into a 1.5-mm. thick plate. The thus-obtained rolled plate was mated with another similar sheet prepared by the same step, with each of their silver layer faces located outwardly, and welded at their mated faces. The two welded plates subsequently were subject to an oxygen atmosphere at a normal atmospheric pressure and at 800 C. for 96 hours. After oxidation being attained, the plates were separated one from another at the welded or mated faces into two separate plate, each of which was punched into disc pieces, each having a 8mm. diameter, thereby producing a composite contact as set forth in the foregoing passage. The thus-obtained composite contact was mounted to an electromagnetic contactor, and tested on contact resistance when wear at the contact face is respectively percent, 25 percent, 50 percent and 75 percent. The same test on contact resistance was applied to the secondly mentioned conventional composite contact (as shown in FIG. 5), which was produced by mating a plate of silver-cadmium alloy with a 1.5mm. thickness, a 30mm. width and a lOOmm. length, with another similar plate of silver-cadmium alloy, welding them at their mated faces, then subjecting them to an oxygen atmosphere at a normal atmospheric pressure and at 800 C. for 72 hours, in a manner that the mated faces are remained unoxidized by 2 mm. in thickness, separating two bonded sheets one from another after oxidation, and punching each sheet into disc pieces each having a 8mm. diameter. Test results on contact resistance of both composite contacts are shown in Table V.

Table V 4 5 Contact resistance Life of both composite contacts is shown in Table Vl. It clearly tells that life of the composite contact of the present invention is increased by 10 percent, in comparison with that of the conventional one.

Table VI Life (hours) The invented composite contact The conventional composite contact As is apparent, the invention resides in a composite electric contact element comprising a contact material formed of an alloy of silver-cadmium oxide, wherein the element has a contact face and an opposite face composed of a silver layer with cadmium oxide particles distributed between the two faces, such that a graded structure of cadmium oxide particles is obtained in which the concentration of the particles increases from a minimum at the contact face to a maximum toward the face with the silver layer. In producing the foregoing electrical contact, an element is formed of an alloy of silver cadmium, one face of which is a contact-forming face, the other face of which has bonded to it a layer ofsilver. ln carrying out'the method, a barrier layer is applied to the contact forming face, the purpose of the barrier layer being to inhibit oxygen diffusion therethrough on the contact face side of the element. The assembly is then subjected to an oxygen atmosphere at an elevated oxygen diffusion temperature in order to oxidize the cadmium in the alloy to form cadmium oxide particles which are distributed throughout the cross section from the silver layer side toward the barrier layer. The barrier layer is thereafter removed from the contact-forming face of the element, whereby to produce a composite electric element having a contact face on one side and a silver layer at the opposite face in which the cadmium oxide particles increase from a minimum at the contact face to a maximum toward the face with the silver layer.

1 claim:

I. A composite electric contact clement comprising a contact material formed of an alloy of silver-cadmium oxide, said element having a contact face and an opposite face composed of a silver layer with cadmium oxide particles distributed in between the two faces such that the concentration of cadmium oxide particles in the contact material increases from a minimum at the contact face to a maximum towards the face with the silver layer.

2. The composite electric contact element of claim 1, wherein the silver layer has a thickness of about one-eighth to one-tenth of the thickness of the contact element.

3. The composite electric contact element of claim 1, wherein the thickness of the silver layer is sufficient to bond the contact to a backing or spring plate. 

2. The composite electric contact element of claim 1, wherein the silver layer has a thickness of about one-eighth to one-tenth of the thickness of the contact element.
 3. The composite electric contact element of claim 1, wherein the thickness of the silver layer is sufficient to bond the contact to a backing or spring plate. 